There are two dates in play -
For bookings after 5/30/24, you can apply member savings to new voyages (5% or 10% depending on VS days).
For sailings departing after 6/5/24, you receive member benefits (such as laundry or upgraded champagne in suite) based on your matched VS days.
According to the T&Cs: (bolding is mine)
Member Level status granted through the Loyalty Status Match Program will be effective on sailings departing on or after June 5, 2024. Notwithstanding the foregoing, VS member savings on future voyages are available on new voyages booked after May 30, 2024, provided a participant has received his or her new Member Level status in VS pursuant to these Loyalty Status Match Program Rules.